This disclosure generally relates to systems for carrying tools across surfaces, such tools including (but not limited to) sensors used in nondestructive inspection (NDI). In particular, this disclosure relates to systems for inspecting a long hollow structure having tapered internal cavities which are difficult to access, especially a structure made of composite material.
A variety of elongated composite structures may have relatively confined internal cavities that require inspection in order to assure that the structure meets production and/or performance specifications. One known elongated composite structure with tapering internal cavities is an integrally stiffened wing box for an airplane. The integrally stiffened wing box is primary structure and as such must be inspected to the required specifications to ensure structural integrity. Both the exterior and interior of each integrally stiffened wing box must be inspected in a production environment. For a production inspection, the inspection rate must be sufficient to meet the part production rate.
The exterior skins of a composite integrally stiffened wing box can be inspected by known conventional methods. Inspection of the vertical support elements (called “spars”) at the part production rate is more challenging due to access limitations, tapering internal cavities, and varying part thickness. The filleted regions that form the transitions between the spar web (i.e., the flat central region of a spar) and the horizontal skins, as well as a small region directly adjacent to each fillet, are scanned by other systems. The problem of scanning the central area of each spar web requires a scanning system located within the confined spaces of long rectangular cavities or tunnels of the integrally stiffened wing box or similar structure. In the case of an integrally stiffened wing box, access is only available from the wider inboard end and the narrow outboard end.
Various prior approaches have been used to perform inspections of the wing box spars. A first approach was manual scanning, in which technicians moved the NDI scanning head over the surface manually. This had several limitations, including: low positioning accuracy and limited reach inside the wing box tunnels. A further prior approach is a single-transducer implementation based on a vehicle that supports a swing-arm device, with the swing arm pivot located on the vehicle at the proximal end of the arm and an ultrasonic transducer at the distal end of the arm. The vehicle moved along the part length from the inboard to the outboard end. During this travel, the swing arm moved the ultrasonic transducer in a vertical arc over the surface of the wall (spar), moving repeatedly back and forth between the upper and lower skins. Reversal of the swing arm motion at both ends of the vertical arc was accomplished using mechanical switches that acted against the upper and lower skins in succession, repeatedly. This device was slow not only because it employed a single transducer but also because the scan pattern involved a large number of motion reversals.
The foregoing solutions do not fully address the scope of the problem to be solved. Accordingly, there is a need for a remote computer-controlled apparatus that can access internal cavities or tunnels of an integrally stiffened wing box or similar elongated hollow structure and produce vertical and horizontal scanning motions of an ultrasonic NDI sensor array to facilitate the inspection of the central web portion of vertical support elements such as spars.